1. Technical Field of the Invention
The present invention relates to mobile communication apparatuses having a built-in type chip antenna for use in mobile communications and local area networks.
2. Related Art of the Invention
A known mobile communication apparatus, for example, a mobile cellular telephone 50, is formed, as shown in FIG. 10, by disposing a circuit board 53 within a case 54. The circuit board 53 is configured in such a manner that a non-directional chip antenna 51 is mounted on one major surface (first major surface) 53a and a ground pattern 52 is provided on the other major surface (second major surface) 53b. Radio waves are received by the chip antenna 51. In this configuration, the chip antenna 51 is electrically connected via a transmission line (not shown) on the circuit board 53 to an RF portion 55 of the cellular telephone 50 disposed on the second major surface 53b. The bandwidth of the chip antenna 51 is determined by the stray capacitance generated between the chip antenna 51 and the ground pattern 52 provided on the second major surface 53b of the circuit board 53.
However, in the above mobile cellular telephone, which serves as a known mobile communication apparatus, since the chip antenna has non-directional characteristics, transmitting radio waves are influenced by a user holding the telephone while using it, thereby deteriorating the antenna characteristics. In order to overcome this drawback, the ground pattern is provided on the second major surface of the circuit board opposite to the first major surface on which the chip antenna is mounted.
However, the following problem is presented. For increasing the bandwidth of the chip antenna, the stray capacitance generated between the chip antenna and the ground pattern provided on the second major surface of the circuit board should be increased. This disadvantageously enlarges the ground pattern, and inevitably also increases the size of the circuit board, resulting in an enlargement of the cellular telephone.
Further, the RF portion of the cellular telephone is mounted on the first major surface of the circuit board, thereby restricting the position at which the ground pattern is formed on the first major surface of the circuit board.